Aluminum as a Catalyst/Reaction Product

[NightHawkInLight]

A recent endeavor of mine was to obtain a large amount of aluminum turnings from a local machine shop. Now that I have finally had the time to try to use the stuff in a practical pyrotechnic way I have had some issues. Although the turnings vary in size most are to thick to mill and have a powder result in any reasonable amount of time. I have attempted to make them more brittle by heating them rapidly with meal ignited under a pile, this has seemed to help slightly but still not well enough to mill down in less than I suspect two weeks. I have not yet tried heating and submersing in oil such as is used to make steel and iron more brittle, I do plan on trying.

On to my thread title: Another thing I tried in an attempt to powder the aluminum was to react it with HCl. I had thought before trying this that the Al might merely be a catalyst, in which case it could be collected once the reaction was completed in a very small particle size. I instead found that it turned into a purple substance that would not collect in a filter. With some internet searching I found that the aluminum is in fact a reactant and turns into AlCl3, a very hygroscopic chemical, so attracted to water that it can explode because of the rapid reaction upon contact. Because I used only ~30% HCl I believe the reaction must have taken place immediately upon formation and turned into the purple solution I witnessed.

Anyway, although this process did not yield aluminum powder as I had hoped it might, it has me believing that there must be a reaction that uses aluminum as either a catalyst, or turns it into a product easily converted back into aluminum in a powder form.

I was unable to find what the reaction between AlCl3 and water produced, but if there were a way to convert it back to aluminum powder it could be useful.

If anyone has anymore ideas to offer on possible reactions, or maybe a way to make aluminum turnings brittle enough to mill a reply would be appreciated.

Also in my case purity is not a large issue, as I want the aluminum suitable for stars and rockets. I do not need the high speed burn for flash, just an attractive spark. If I get any results I'll be sure to post them.

[asilentbob]

Its called the activity series of metals, learn to use it.

 

Al(s) + HCl(aq) ---> AlCl3(aq) + H2(g)

AlCl3(aq) + Mg(s) ---> MgCl2(aq) + Al(s)

 

Basicly any metal more reactive (higher up on the chart) than your starting metal will switch places with your metal. However obviously with the very reactive metals like lithium or sodium they would react with the water to a great extent too and greatly lower yield. The above reactions can work... but they are rarely used. Mostly because expending magnesium to make aluminum is so backwards. Also the aluminum that precipitates will react with the water to an extent... so really its not worth it.

 

What were you milling with? IE material, shape, OD, weight, etc... Big heavy chrome plated steel balls are one of the preferred milling medias for grinding down hard materials like other metals. Fishing weights just wont cut it and you would get ALOT more lead impurity than with BP milling for example... Plus metal milling in general does indeed take a long time in most circumstances... unless the material is really brittle... like MgAl!

 

When it comes to powdering metals really the easiest way to go would be to alloy Mg and Al 50/50 and powder it... its brittle... like glass... and its such a beautiful metal alloy anyways...

[NightHawkInLight]

Hmm, I have just looked up a reactivity chart and the next step above Mg is calcium, and then above that is sodium. Obviously neither of those commonly exist in a pure form in nature because of the reactivity. So perhaps there is a sodium or calcium salt/other common chemical that would dissociate into the base elements upon reacting with HCl so it could be added to a solution once all the aluminum had reacted and take its place. Reacting Al with a liquid that would also react with the Cl in table salt comes to mind as a perfectly simple (although probably nonexistent) reaction.

Although the HCl reaction with aluminum is what i was focused on in my first post, I don't want to limit it to that. Any reaction that would use the aluminum and then form a product that could be reacted back to the original metal (hopefully without using a more expensive substance) would be good to know.

As I said a reaction where the Al would act as a catalyst would be ideal because no other reaction would be needed. I realize a reaction like this is probably uncommon to say the least, and would probably require a large reaction temp. and already powdered or molten Al.

 

I may try making some MgAl once i buy more Mg, all I have is powder and I don't consider it worth it to melt it down. I mill with quarters at the moment, however there is just no way I will be able to mill metals in my current mill with any media. It is far to small and long overdue for an update. Hopefully by the end of this year.

 

Thanks for the reply

[Mumbles]

No reaction as you describe exists. In order for aluminum to be precipitated as the metal, there must be a redox reaction. Reacting anything with HCl, will by default render it useless for a redox reaction with the aluminum ions.

 

I would suggest the sand paper reaction. It's similar to the sandmeyer reaction, only it involves a block of aluminum and some sand paper instead of aromatic azo compounds.

 

The point is, the only practical way, on a home scale, to produce aluminum powder is to reduce it by mechanical means. No chemical reaction will give you the product you desire.

[psyco_1322]

Or the get a job and buy some reaction! Thats amazingly fast!

 

Oh and you can pick up some rather large chunks of Mg for your redox reaction purposes at your local "big" recyling yards, military is always getting ride of some. And people bring it in a lot mistaking it as Al. Just ask and buy!

[NightHawkInLight]

Yeah...I figured that would probably be the case about 5 minutes after posting this topic Mumbles, but it was worth a shot. In the meantime is there any way to make the aluminum shavings I have more brittle without making a MgAl alloy? Like I said in my first post I don't mind mild contaminants such as motor oil or carbon, so long as the Al is still flammable with an oxidizer.

 

psyco_1322: "Or the get a job and buy some reaction! Thats amazingly fast!"

If that's a joke I don't get it. Thanks for the suggestion for where to find some scrap Mg, whenever I can buy directly instead of ordering online I'll take it.

[Bonny]

A coffee grinder will chew up some of the finer Al shavings and then they can be seived to size, discarding the really large particles. If you have a large powerful coffee grinder,should work even better. I've successfully used drill shavings and produced up to -100mesh Al powder. I imagine you might be able to further mill the particles in a ball mill after grinding in a coffee mill.

[NightHawkInLight]

That's a good idea, I'd have to take some of the larger pieces out though. Some are quite thick, industrial lathes aren't exactly a powder making implement.

[Bonny]

Another great source of Al is from bandsaw cuttings. If you have a good connection at the machine shop, they might save some for you, although they are likely to be contaminated with steel etc... I get most of my coarse Al from a bandsaw I have at work. It can be seived easily (as is) to -100mesh maybe finer, or ball milled to even finer grades.